Display for SystemTime

src/libstd/lib.rs

@@ -295,6 +295,7 @@
 #![feature(staged_api)]
 #![feature(stmt_expr_attributes)]
 #![feature(str_internals)]
+#![feature(system_time_display_iso_8601)]
 #![feature(rustc_private)]
 #![feature(thread_local)]
 #![feature(toowned_clone_into)]

src/libstd/time/iso_8601.rs

@@ -0,0 +1,328 @@
+use fmt;
+use time::Duration;
+
+
+// Number of seconds in a day is a constant.
+// We do not support leap seconds here.
+const SECONDS_IN_DAY: u64 = 86400;
+
+
+// Gregorian calendar has 400 years cycles, this is a procedure
+// for computing if a year is a leap year.
+fn is_leap_year(year: i64) -> bool {
+    if year % 4 != 0 {
+        false
+    } else if year % 100 != 0 {
+        true
+    } else if year % 400 != 0 {
+        false
+    } else {
+        true
+    }
+}
+
+fn days_in_year(year: i64) -> u32 {
+    if is_leap_year(year) {
+        366
+    } else {
+        365
+    }
+}
+
+
+// Number of leap years among 400 consecutive years.
+const CYCLE_LEAP_YEARS: u32 = 400 / 4 - 400 / 100 + 400 / 400;
+// Number of days in 400 years cycle.
+const CYCLE_DAYS: u32 = 400 * 365 + CYCLE_LEAP_YEARS;
+const CYCLE_SECONDS: u64 = CYCLE_DAYS as u64 * SECONDS_IN_DAY;
+
+
+// Number of seconds between 1 Jan 1970 and 1 Jan 2000.
+// Check with:
+// `TZ=UTC gdate --rfc-3339=seconds --date @946684800`
+const YEARS_1970_2000_SECONDS: u64 = 946684800;
+// Number of seconds between 1 Jan 1600 and 1 Jan 1970.
+const YEARS_1600_1970_SECONDS: u64 = CYCLE_SECONDS - YEARS_1970_2000_SECONDS;
+
+
+// For each year in the cycle, number of leap years before in the cycle.
+static YEAR_DELTAS: [u8; 401] = [
+     0,  1,  1,  1,  1,  2,  2,  2,  2,  3,  3,  3,  3,  4,  4,  4,  4,  5,  5,  5,
+     5,  6,  6,  6,  6,  7,  7,  7,  7,  8,  8,  8,  8,  9,  9,  9,  9, 10, 10, 10,
+    10, 11, 11, 11, 11, 12, 12, 12, 12, 13, 13, 13, 13, 14, 14, 14, 14, 15, 15, 15,
+    15, 16, 16, 16, 16, 17, 17, 17, 17, 18, 18, 18, 18, 19, 19, 19, 19, 20, 20, 20,
+    20, 21, 21, 21, 21, 22, 22, 22, 22, 23, 23, 23, 23, 24, 24, 24, 24, 25, 25, 25, // 100
+    25, 25, 25, 25, 25, 26, 26, 26, 26, 27, 27, 27, 27, 28, 28, 28, 28, 29, 29, 29,
+    29, 30, 30, 30, 30, 31, 31, 31, 31, 32, 32, 32, 32, 33, 33, 33, 33, 34, 34, 34,
+    34, 35, 35, 35, 35, 36, 36, 36, 36, 37, 37, 37, 37, 38, 38, 38, 38, 39, 39, 39,
+    39, 40, 40, 40, 40, 41, 41, 41, 41, 42, 42, 42, 42, 43, 43, 43, 43, 44, 44, 44,
+    44, 45, 45, 45, 45, 46, 46, 46, 46, 47, 47, 47, 47, 48, 48, 48, 48, 49, 49, 49, // 200
+    49, 49, 49, 49, 49, 50, 50, 50, 50, 51, 51, 51, 51, 52, 52, 52, 52, 53, 53, 53,
+    53, 54, 54, 54, 54, 55, 55, 55, 55, 56, 56, 56, 56, 57, 57, 57, 57, 58, 58, 58,
+    58, 59, 59, 59, 59, 60, 60, 60, 60, 61, 61, 61, 61, 62, 62, 62, 62, 63, 63, 63,
+    63, 64, 64, 64, 64, 65, 65, 65, 65, 66, 66, 66, 66, 67, 67, 67, 67, 68, 68, 68,
+    68, 69, 69, 69, 69, 70, 70, 70, 70, 71, 71, 71, 71, 72, 72, 72, 72, 73, 73, 73, // 300
+    73, 73, 73, 73, 73, 74, 74, 74, 74, 75, 75, 75, 75, 76, 76, 76, 76, 77, 77, 77,
+    77, 78, 78, 78, 78, 79, 79, 79, 79, 80, 80, 80, 80, 81, 81, 81, 81, 82, 82, 82,
+    82, 83, 83, 83, 83, 84, 84, 84, 84, 85, 85, 85, 85, 86, 86, 86, 86, 87, 87, 87,
+    87, 88, 88, 88, 88, 89, 89, 89, 89, 90, 90, 90, 90, 91, 91, 91, 91, 92, 92, 92,
+    92, 93, 93, 93, 93, 94, 94, 94, 94, 95, 95, 95, 95, 96, 96, 96, 96, 97, 97, 97, 97,
+];
+
+
+/// UTC time
+pub struct TmUtc {
+    /// Year
+    year: i64,
+    /// 1..=12
+    month: u32,
+    /// 1-based day of month
+    day: u32,
+    /// 0..=23
+    hour: u32,
+    /// 0..=59
+    minute: u32,
+    /// 0..=59; no leap seconds
+    second: u32,
+    /// 0..=999_999_999
+    nanos: u32,
+}
+
+impl TmUtc {
+
+    fn day_of_cycle_to_year_day_of_year(day_of_cycle: u32) -> (i64, u32) {
+        debug_assert!(day_of_cycle < CYCLE_DAYS);
+
+        let mut year_mod_400 = (day_of_cycle / 365) as i64;
+        let mut day_or_year = (day_of_cycle % 365) as u32;
+
+        let delta = YEAR_DELTAS[year_mod_400 as usize] as u32;
+        if day_or_year < delta {
+            year_mod_400 -= 1;
+            day_or_year += 365 - YEAR_DELTAS[year_mod_400 as usize] as u32;
+        } else {
+            day_or_year -= delta;
+        }
+
+        (year_mod_400, day_or_year)
+    }
+
+    // Convert seconds of the day of hour, minute and second
+    fn seconds_of_day_to_h_m_s(seconds: u32) -> (u32, u32, u32) {
+        debug_assert!(seconds < SECONDS_IN_DAY as u32);
+
+        let hour = seconds / 3600;
+        let minute = seconds % 3600 / 60;
+        let second = seconds % 60;
+
+        (hour, minute, second)
+    }
+
+    // Convert day of year (0-based) to month and day
+    fn day_of_year_to_month_day(year: i64, day_of_year: u32) -> (u32, u32) {
+        debug_assert!(day_of_year < days_in_year(year));
+
+        let days_in_months = if is_leap_year(year) {
+            &[31, 29, 31, 30, 31, 30, 31, 31, 30, 31, 30, 31]
+        } else {
+            &[31, 28, 31, 30, 31, 30, 31, 31, 30, 31, 30, 31]
+        };
+
+        let mut rem_days = day_of_year;
+        let mut month = 1;
+        while rem_days >= days_in_months[month - 1] {
+            rem_days -= days_in_months[month - 1];
+            month += 1;
+        }
+
+        debug_assert!(rem_days + 1 <= days_in_months[month - 1]);
+
+        (month as u32, rem_days + 1)
+    }
+
+    // Construct from duration added to cycle start year
+    fn from_cycle_start_add_duration(mut cycle_start: i64, add: Duration) -> TmUtc {
+        debug_assert!(cycle_start % 400 == 0);
+
+        // Split duration to days and duration within day
+
+        let days = add.as_secs() / SECONDS_IN_DAY;
+        let duration_of_day = add - Duration::from_secs(days * SECONDS_IN_DAY);
+
+        let cycles = days / CYCLE_DAYS as u64;
+        cycle_start += cycles as i64 * 400;
+        let day_of_cycle = days % CYCLE_DAYS as u64;
+
+        let (year_mod_400, day_of_year) =
+            TmUtc::day_of_cycle_to_year_day_of_year(day_of_cycle as u32);
+
+        let (year,) = (cycle_start + year_mod_400,);
+        let (month, day) = TmUtc::day_of_year_to_month_day(year, day_of_year);
+        let (hour, minute, second) =
+            TmUtc::seconds_of_day_to_h_m_s(duration_of_day.as_secs() as u32);
+
+        TmUtc {
+            year,
+            month,
+            day,
+            hour,
+            minute,
+            second,
+            nanos: duration_of_day.subsec_nanos(),
+        }
+    }
+
+    // Construct from duration added to epoch
+    pub fn from_epoch_add(add: Duration) -> TmUtc {
+        // Special case to prevent integer overflow in duration addition
+        if add > Duration::from_secs(YEARS_1970_2000_SECONDS) {
+            TmUtc::from_cycle_start_add_duration(
+                2000, add - Duration::from_secs(YEARS_1970_2000_SECONDS))
+        } else {
+            TmUtc::from_cycle_start_add_duration(
+                1600, add + Duration::from_secs(YEARS_1600_1970_SECONDS))
+        }
+    }
+
+    // Construct from duration subtracted from epoch
+    pub fn from_epoch_sub(mut sub: Duration) -> TmUtc {
+
+        // Make `sub` less than 400 years
+
+        // Number of full leap cycles in `sub`
+        let leap_cycles = sub.as_secs() / CYCLE_SECONDS;
+        let year = 1970 - (leap_cycles * 400) as i64;
+        sub -= Duration::from_secs(leap_cycles * CYCLE_SECONDS);
+
+        // Convert subtraction to addition
+        // and align year to a cycle start
+
+        // `year` is still 370 years ahead of cycle start.
+        debug_assert!((year % 400 + 400) % 400 == 370);
+
+        // Subtract 370 years to get to cycle start
+        // and additional 400 year to prevent integer underflow in duration subtraction
+        let cycle_start = year - 400 - 370;
+        let add_from_cycle_start =
+            Duration::from_secs(CYCLE_SECONDS + YEARS_1600_1970_SECONDS) - sub;
+
+        debug_assert!(cycle_start % 400 == 0);
+
+        return TmUtc::from_cycle_start_add_duration(cycle_start, add_from_cycle_start);
+    }
+
+    pub fn fmt_iso_8601(&self, f: &mut fmt::Formatter) -> fmt::Result {
+        if self.year > 9999 {
+            // ISO-8601 extended format requires leading plus
+            write!(f, "+{}", self.year)?;
+        } else if self.year < 0 {
+            // At least 4 digits
+            write!(f, "{:05}", self.year)?;
+        } else {
+            write!(f, "{:04}", self.year)?;
+        }
+
+        write!(f, "-{:02}-{:02}T{:02}:{:02}:{:02}",
+            self.month, self.day, self.hour, self.minute, self.second)?;
+
+        // if width is not specified, print nanoseconds
+        let subsec_digits = f.precision().unwrap_or(9);
+        if subsec_digits != 0 {
+            let width = if subsec_digits > 9 { 9 } else { subsec_digits };
+
+            // "Truncated" nanonseconds.
+            let mut subsec = self.nanos;
+
+            // Performs 8 iterations when width=1,
+            // but that's probably not a issue compared to other computations.
+            for _ in width..9 {
+                subsec /= 10;
+            }
+
+            write!(f, ".{:0width$}", subsec, width=width as usize)?;
+
+            // Adding more than 9 digits is meaningless,
+            // but if user requests it, we should print zeros.
+            if subsec_digits > 9 {
+                write!(f, "{:0n$}", 0, n=subsec_digits - 9)?;
+            }
+        }
+
+        write!(f, "Z")
+    }
+}
+
+#[cfg(test)]
+mod test {
+    use super::*;
+    use time::Duration;
+    use fmt;
+    use u64;
+
+    struct TmUtcDisplayIso8601(TmUtc);
+
+    impl fmt::Display for TmUtcDisplayIso8601 {
+        fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
+            self.0.fmt_iso_8601(f)
+        }
+    }
+
+    #[test]
+    fn test_fmt() {
+        fn test_impl(expected: &str, secs: i64, nanos: i32, subsec_digits: u32) {
+            if nanos != 0 {
+                assert_eq!(secs >= 0, nanos >= 0);
+            }
+
+            let time = TmUtcDisplayIso8601(if secs >= 0 {
+                TmUtc::from_epoch_add(Duration::new(secs as u64, nanos as u32))
+            } else {
+                TmUtc::from_epoch_sub(Duration::new(-secs as u64, -nanos as u32))
+            });
+
+            assert_eq!(expected, format!("{:.digits$}", time, digits=subsec_digits as usize));
+        }
+
+        // Tests can be validated with with GNU date:
+        // `TZ=UTC gdate --date @1535585179 --iso-8601=seconds`
+
+        test_impl("1970-01-01T00:00:00Z", 0, 0, 0);
+        test_impl("2018-08-29T23:26:19Z", 1535585179, 0, 0);
+        test_impl("2018-08-29T23:26:19.123Z", 1535585179, 123456789, 3);
+        test_impl("1646-04-01T03:45:44Z", -10216613656, 0, 0);
+        // Last day of year in regular and leap year
+        test_impl("2018-12-31T00:00:00Z", 1546214400, 0, 0);
+        test_impl("2020-12-31T00:00:00Z", 1609372800, 0, 0);
+        // More than 9 digits in precision
+        test_impl("1970-01-01T00:00:00.000000001000Z", 0, 1, 12);
+        // Large years
+        test_impl("5138-11-16T09:46:40Z", 100000000000, 0, 0);
+        // Leading zero
+        test_impl("0000-12-31T00:00:00Z", -62135683200, 0, 0);
+        // Minus zero
+        test_impl("-0003-10-30T14:13:20Z", -62235683200, 0, 0);
+        // More than 4 digits
+        test_impl("+33658-09-27T01:46:41Z", 1000000000001, 0, 0);
+        // Largest value GNU date can handle
+        test_impl("+2147485547-12-31T23:59:59Z", 67768036191676799, 0, 0);
+        // Negative dates
+        test_impl("1969-12-31T23:59:59Z", -1, 0, 0);
+        test_impl("1969-12-31T23:59:00Z", -60, 0, 0);
+        test_impl("1969-12-31T23:59:58.900Z", -1, -100_000_000, 3);
+        test_impl("1966-10-31T14:13:20Z", -100000000, 0, 0);
+        test_impl("-29719-04-05T22:13:19Z", -1000000000001, 0, 0);
+        // Smallest value GNU date can handle
+        test_impl("-2147481748-01-01T00:00:00Z", -67768040609740800, 0, 0);
+    }
+
+    #[test]
+    fn test_fmt_max_duration() {
+        let duration = Duration::new(u64::max_value(), 999_999_999);
+        // Simply check that there are no integer overflows.
+        // I didn't check that resulting strings are correct.
+        assert_eq!("+584554051223-11-09T07:00:15.999999999Z",
+            format!("{}", TmUtcDisplayIso8601(TmUtc::from_epoch_add(duration))));
+        assert_eq!("-584554047284-02-23T16:59:44.000000001Z",
+            format!("{}", TmUtcDisplayIso8601(TmUtc::from_epoch_sub(duration))));
+    }
+}